In the handling of thin objects and especially flat objects with regular or irregular outlines for a variety of purposes, especially skins in tanneries or the like, means have been provided for laying the flat object upon a receiving surface and/or stacking the objects upon such surfaces.
In the mechanization of tannery processes and especially the handling of skins therein, considerable difficulties have been encountered because of the nature of the object and the manner in which it must be deposited or stacked.
Apparatus has been proposed heretofore for manipulating, e.g. automatically stacking, skins without considerable success. It should be noted, however, that improvements in apparatus for the stacking of skins, with which the present application is particularly concerned, are not limited in applicability to these objects but can be used for the handling of other thin, flat objects such as certain wood products in the wood industry.
In the tanning industry the skins are displaced successively on or in the treatment machines (surface treatment, pistoletting, drying, measuring etc.) by endless conveyor belts. These conveyor belts can be constituted by parallel wires which are independent from one another but are sufficiently close together to provide the necessary support while permitting the passage of air and light.
In order to deposit the skins, it is necessary to raise the wire conveyor, if possible before it reaches the return roller, to avoid wedging the skin between the wires and this roller and thereby damaging the skin or the apparatus. The skins must be deposited by the apparatus upon a table, a pallet or a frame or horse. It is also a common requirement that the skins alternately be reversed to deposit the flesh side of one skin against the flesh side of another and the grain side against grain side. This mode of stacking is known as a "marriage" of the skins.
As previously indicated, several devices have been proposed to carry out this type of stacking and skin-depositing, but all have drawbacks. Certain of these devices utilize endless bands while others employ fork-like members to lay down the skins. The principal disadvantages of these devices are the following:
(a) The displacement of the skins on their conveyors is unreliable; PA1 (b) the speed of the skin at the moment at which it is deposited, relative to the receiving surface, is not zero so that the stacking is unreliable; and PA1 (c) the apparatus generally comprises carriages and other elements actuated with rapid and sharp reversing movements which give rise to shocks in the mechanism and a high degree of wear and tear.
The apparatus designed for the depositing and stacking of flat objects, e.g. sheets of paper, is known and has some of the capabilities required for an apparatus intended to stack or deposit skins in tanneries or the like. These systems use an endless belt conveyor having a run or stretch, one end of which is fixed with respect to the receiving surface while the other end is retractable under the object to be deposited. This principle is highly effective because it theoretically permits the deposition of the object at zero velocity. However, the apparatus is highly complex and, when applied to the stacking of skins, tends to fold them or pinch them accidentally between the belts or cables forming the endless conveyor surface and the return drum or rollers.